text: # -*- coding: utf-8 -*-
  # pylint: disable=invalid-name
  
  # Copyright 2017 IBM RESEARCH. All Rights Reserved.
  #
  # Licensed under the Apache License, Version 2.0 (the "License");
  # you may not use this file except in compliance with the License.
  # You may obtain a copy of the License at
  #
  #     http://www.apache.org/licenses/LICENSE-2.0
  #
  # Unless required by applicable law or agreed to in writing, software
  # distributed under the License is distributed on an "AS IS" BASIS,
  # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  # See the License for the specific language governing permissions and
  # limitations under the License.
  # =============================================================================
  
  """
  Pauli Z (phase-flip) gate.
  """
  from qiskit import CompositeGate
  from qiskit import Gate
  from qiskit import InstructionSet
  from qiskit import QuantumCircuit
  from qiskit import QuantumRegister
  from qiskit.extensions.standard import header  # pylint: disable=unused-import
  
  
  class ZGate(Gate):
      """Pauli Z (phase-flip) gate."""
  
      def __init__(self, qubit, circ=None):
          """Create new Z gate."""
          super().__init__("z", [], [qubit], circ)
  
      def qasm(self):
          """Return OPENQASM string."""
          qubit = self.arg[0]
          return self._qasmif("z %s[%d];" % (qubit[0].openqasm_name, qubit[1]))
  
      def inverse(self):
          """Invert this gate."""
          return self  # self-inverse
  
      def reapply(self, circ):
          """Reapply this gate to corresponding qubits in circ."""
          self._modifiers(circ.z(self.arg[0]))
  
  
  def z(self, q):
      """Apply Z to q."""
      if isinstance(q, QuantumRegister):
          instructions = InstructionSet()
          for j in range(q.size):
              instructions.add(self.z((q, j)))
          return instructions
  
      self._check_qubit(q)
      return self._attach(ZGate(q, self))
  
  
  QuantumCircuit.z = z
  CompositeGate.z = z
  